May of todays battery-operated consumer products drain energy from the batteries at high rates. These high drain rates make the device particularly suitable for rechargeable batteries and, for user convenience, many products sold today contain internal circuiting for charging the rechargeable batteries while they are installed in the energy using device.
Because rechargeable batteries, such as nickel cadmium batteries, are sold in the same AA, C and D sizes as are primary (non-rechargeable) batteries, either primary or rechargeable batteries may be inserted into the energy using device. However, since most primary batteries may not be safely recharged, extreme care must be taken to insure that the charging circuit will provide recharging current only when a rechargeable battery is inserted in the energy-using device and will not provide recharging current when a primary battery is inserted in the energy-using device.
U.S. Pat. No. 4,147,838 issued to Edward A. Leffingwell discloses a concept for recharging only a rechargeable battery in an energy-using device which will accept either a rechargeable battery or a primary battery. This patent teaches a separate charging terminal contact on the rechargeable battery which engages a corresponding charging terminal in the energy-using device. The charging terminal contact is spaced from the power terminal contacts on the battery and engages the corresponding charging terminal of the energy-using device in a location remote from the power terminal contacts. Since a primary battery does not have a charging terminal contact in the same location, the structure disclosed in the above-referenced patent insures that a primary battery will not be recharged when inserted in the energy-using device. The present invention is an improvement upon the structure disclosed in the above-referenced patent.
Typical AA, C and D size batteries are generally cylindrical in shape; that is to say, they extend circumferentially about and axially along a central axis and have one power terminal contact at one end of the cylinder and another power terminal contact at the other end of the cylinder. Because of this cylindrical shape the battery may be inserted in the energy-using device in a number of different rotational positions. More specifically, while the battery must be inserted so as to be axially aligned with the axially extending cavity in which the battery resides in the energy-using device, the battery may be rotated about its axis and installed in the cavity in the energy-using device in one of any number of rotational positions. Accordingly, use of a terminal contact of the type taught in the aforementioned patent on the circumferentially extending outer surface of the battery makes it possible that engagement between the charging terminal contact on the battery and the corresponding charging contact in the energy-using device may not be effected. The present invention addresses this problem and provides a solution which insures that engagement is always effected.